Internal and external jack assembly for telescopic caissons



May 16, 1961 2,984,075

INTERNAL AND EXTERNAL JACK ASSEMBLY FOR TELESCOPIC CAISSONS G. 1-: SUDEROW 2 Sheets-Sheet 1 Original Filed Dec. 30, 1954 F/GJ.

3 H -u I II 3 .l I mH l I m/ Fru I 1 il H 4 l7 .L. 2 W 8 2 3 9 H l l 7 k 1 6 a I I N w 4 4 5 l 8 I 3 Q 5 l 2 7 9 8 5 4 2 8 INVENTOR GEORGE E. SUDEROW ATTORNEY May 16, 1961 s. E. SUDEROW 2,984,075

INTERNAL AND EXTERNAL JACK ASSEMBLY FOR TELESCOPIC CAISSONS Original Filed Dec. 30, 1954 2 Sheets-Sheet 2 1 63 m 1' so 4 al 64 A x 30 54 |6 r ,54 77 43 4| 7 36 67 74 75 76 rfl W1- 66 GI' 63 42 38 30 59 I5 44( 34 a 2 48 is 53 m 32 7 66 7| w 70 49 I6 7 H l6 4? f: E 60 INVENTOR 2; GEORGE ESUDEROW 55 I 67 75 74 18: BY

INTERNAL AND EXTERNAL JACK ASSEMBLY FOR TELESCOPIC CAISSONS George E. Suderow, New York, N.Y., assignor to De atent O Long Corporation, New York, N.Y., a corporation of Delaware Continuation of application Ser. No. 502,313, Apr. 19,

1955, and a divisionof application Ser. No. 478,627,

Dec. 30, 1954. This application May 15, 1956, Ser. No. 584,962

22 Claims. (Cl. 61-465) The present invention relates to a combined barge and working platform assembly, and, more particularly, to a jack mechanism associated with telescopic caissons or columns for moving and supporting the barge above the level of the water.

This application is a continuation of my copending application, Serial No. 502,313, filed April 19, 1955, now abandoned, and a division of my copending application, Serial No. 478,627, filed December 30, 1954.

An important object consists in associating with the barge spaced telescopic caissons or columns, with each of which is operatively associated an external jack mechanism and one or more internal jack mechanisms for moving the sections of the telescopic caissons vertically.

A further object consists in forming each of the well openings of the barge or supporting member with a chamber in which is housed an external pin jack mechanism arranged releasably to engage openings in the upper sections of each telescopic caisson. The intermediate and lower sections of each caisson have mounted on the top thereof an internal pin jack mechanism which coacts with the external jack mechanism to move each caisson section vertically either to collapse or extend the sections.

Other objects and advantages of the invention will become apparent from the following description when taken in conjunction with the accompanying claims and drawings.

Referring to the drawings in which is shown a preferred embodiment of the invention:

Figure 1 is a side view of a floating barge or other type of marine platform constructed in accordance with the present invention, with parts in section, and showing one of the telescopic sectional caissons or columns in its stowed or nested position and another telescopic caisson in its extended position;

Figure 2 is an enlarged detailed sectional view showing the telescopic caisson sections in their extended position;

Figure 3 is a sectional view taken substantially along the line 3-3 of Figure 2;

Figure 4 is a sectional view taken substantially along the line 4-4 of Figure 2; and

Figure 5 is an enlarged, detailed, sectional view of a locking pin assembly associated with the external jack mechanism.

1n the drawings, .10 indicates .an elongated floating barge or other type of platform of any suitable length and width. The barge is provided with horizontally spaced vertical well openings 11 (Figure 1) through which extend the telescopic caissons or supporting columns 12 of any suitable size and cross-sectional configuration. Each caisson or column 12 is preferably formed with an outer upper end section 13, a lower inner end section 14, and one or more intermediate interfitting inner sec tions 15' (Figure, 2) so as to be of any desired length. The upper section 13 and each of the intermediate sections 15 are provided with diametrically disposed vertical I rows of pin-receivingopenings '16. These pin openings Patented May 16, 1961 "a vertically spaced lower circular wall 20 (Figure 2).

An outer, enlarged, concentric wall 21 encloses the walls 19 and 20. Horizontal or transverse annular abutment members or plates 22 and 23 are connected to the inner Walls 19 and 20 as well as the outer wall 21 in any suitable manner, such as by welding as at 24. A vertically disposed, circular stitfening plate or wall 25 extending between the plates 22 and 23 may be provided to further strengthen the walls of each chamber 17. An annular, reinforcing, transverse plate 26 having a central opening is positioned beneath the plate 23 and is spaced above the bottom of the barge 10 to form a recess 27. The plate 26 is maintained in a fixed position in any suitable manner, such as by welding as at 24.

Each of the external jack mechanisms 18 includes an upper pin assembly 28 and a lower pin assembly 29 (Figure 2) which are substantially similar in construction and operation so that only one will be specifically described. Each of the pin assemblies 28 and 29 has an annular inner sleeve or memberv 30 in vertical alignment with the circular walls 19 and 20. Each sleeve 30 is connected to a pair of vertically spaced, flat, annular, horizontal plates or ring members 31 by welding as 'at 32 (Figure 5). Concentric with the sleeve 30 and also secured to the members 31 is an outer sleeve or ring member 33. Thehinner and outer sleeves 30 and 33 are provided with diametrically disposed openings 34 through which extend aligned casings 35 of the upper pin assembly 28 and the lower pin assembly 29. A reciprocating locking pin or bolt 36 (Figure 5) extends horizontally through bearing block 37 of each of the '38 and the end 43 of the casing 35 to urge the pin 36 to extend while any suitable fluid under pressure such as oil, gas, or the like, is introduced into the motor 40 through the flexible tubing or conduit 44 from a suitable source of supply (not shown) to urge the pin 36 to retract.

Between the lower annular flat ring member 31 of the upper pin assembly 28 and the upper member 31 of the lower assembly 29, are circumferentially spaced, fluid operated, double acting motors 45, each of which includes a vertical cylinder 46 which is connected or Welded to the upper member 31 of the lower assembly 29. Each cylinder 46 has a piston rod 47 terminating in a threaded end 48 (Figure 5) which extends through an opening in the lower ring member 31 of the upper assembly 28 so as to be fixed thereto by the nuts 49 and 50 disposed on opposite sides of the latter member 31. Each of the cylinders 46 communicates at the opposite ends thereof through the flexible tubing or conduits 51 and 52, with a suitable source of fluid pressure so that the piston rods 47 may be actuated to move the upper and lower pin assemblies towards or away from each other.

Each of the intermediate sections 15, as well as the lower end section 14 of each perforated caisson 12, is provided with an internal pin jack mechanism similar in construction'and operation to the external jack mechanism 18, previously described. Each internal jack mechanism includes an upper .pin assembly 53 and alower pin assembly 54, which are substantially identical, so that only one will be specifically, described. Each of the assem- -operated motor 62 (Figure 2).

ber 55 and a concentric, outer sleeve 56 between which are disposed vertically extending reinforcing plates 57 and auxiliary reinforcing plates 58 (Figure 3). At diametrically opposite points, the inner sleeve 55 and the outer sleeve 56 have transverse aligned openings through which extend the casings 59 of the upper and lower pin assemblies. Extending outwardly from each of the easings 59 is a reciprocating locking pin or bolt 60 arranged to be inserted into an opening 16 in an adjacent section of the caisson when the bolt is moved into registration therewith so as to releasably lock the caisson sections in a fixed position. Each pin 60 is connected to the stem 61 of a reciprocating piston 61' of a fluid Fluid under pressure is conducted to each of the motors 62 by the flexible tubing 63 to retract the corresponding pin 60. A coil compression spring 64 confined between the pin 60 and the end 65 of the casing 59 (Figure 3) acts to extend the bolt 60 when the fluid pressure in the motor 62 is withdrawn.

The upper and lower pin assemblies 53 and 54 are provided with pairs of vertically spaced, horizontal, flat annular members or rings 66 and 67, respectively, similar to the horizontal pair of members 31, previously described. A series of circumferentially spaced, upright, double acting fluid motors 68 are positioned between the upper and lower pin assemblies 53 and 54, and each motor includes a casing 69 which is connected to an adjacent horizontal ring member 67 of the lower pair and has its piston rod 70 connected as at 71 to the adjacent annular member 66 of the upper pair so as to move the upper and lower pin assemblies of each section either towards or away from each other when the pins 60 of one of the assemblies are released from engagement with the openings in the caissons. Fluid under pressure is conducted to each of the cylinders 69 through the flexible conduits 72 and 73 which function as a supply and also as exhaust means for withdrawing the fluid from each cylinder 69.

The upper section 13 of each caisson is provided with an open lower end into which extends the closed end or top 74 of an intermediate section 15, which preferably is reinforced by a diametric stiffening plate 75. The lower pin assembly 54 of the corresponding internal jack mechanism is fixed to the top 74, as by welding or other means suitably securing the lower member 67 of the pair to the top 74. The lower open end of the upper section 13 is provided with an interior annular ring or shoulder 76 which is connected to the inner wall thereof in any suitable manner such as by welding or the like, and which coacts with a similarly formed exterior ring or shoulder 77 connected to the upper end of the intermediate section 15, to constitute a stop for limiting the downward movement of the intermediate section so as to prevent complete separation of the sections 13 and 15 when extended. Each of the intermediate sections 15 is similarly formed at its lower end with a suitable interior ring 78 which coacts with a complementary exterior stop ring 79 on the upper end of the next lower section for limiting the downward movement of the latter. The lower end section '14 is similarly provided with a top 74 on which is fixed the adjacent lower pin assembly and which is provided with a reinforcing plate 75. The lower end section 14 may also be provided with the telescopic tank footing members 80, 81, and 82 which are described more specifically in my copending application, Serial No. 469,092, filed November 16, 1954.

The operation of the external jack mechanism 18 is substantially similar to that of the jack mechanisms disclosed in the copending applications of Pointer, Serial No. 143,627, filed February 11, 1950, now abandoned, and Serial No. 283,567, filed April 22, 1952; and also the Suderow applications, Serial No. 378,103, filed Septem- 1531542, 1953, and Serial No. 478,627, filed December 30,

Thus, it will be seen that the parts, when in their normal and inoperative position, are nested as shown in section in Figure 1, with the sections 14 and 15 telescoping within the section 13 and the sections 80, 81, and 82 of the footing members nested in the recess 27. Each of the motors 40, 45, 53, and 68 is connected by the flexible tubings 44, 51, 52, 63, 72, and 73 to a suitable source of fluid under pressure carried by the barge. On the deck of the barge and conveniently located for manual operation are master control means (not shown) by which any one section of a caisson may be actuated or all of the sections of all the caissons may be simultaneously operated.

Assuming the parts are in their stowed position, as shown in section in Figure 1, there is no fluid pressure in the motors 40 and 62, so that the expansion springs 41 and 64 urge the locking pins outwardly into aligned openings 16 in the sections of each caisson to maintain the caisson sections and footing members firmly in their nested position. To move the telescopic caissons from their stowed position to their extended position, the internal jack mechanism mounted on the top of the lower section 14 of the caisson is operated so that the lower section 14 with its telescopic footing 80, 81, and 82 is extended downwardly at least to the extent where the footing can become fully operative, i.e., extensible. Thereupon, the internal and external jack mechanisms are appropriately operated to extend the caissons and/or move the upper section downwardly relative to the barge until the footings engage the marine bottom 83 (Figure 1) and are imbedded therein sufficiently to support the weight of the barge 10. Continued extension of the caissons, or forcing the upper caisson section downwardly relative to the barge, will then serve to raise the barge out of the water.

In operating an internal jack mechanism to extend or lower the section to which it is secured, and starting with the motor 68 extended and the pins 60 of both assemblies 53 and 54 extended, fluid pressure is first applied through the flexible tubing 63 to the motors 62 of the upper assembly 53, thus disengaging their pins 60 from the outer caisson section. The motors 68 are then operated to retract their piston rods 70, thus lowering the upper pin assembly 53. As soon as the piston rods 70 are retracted enough so that the pins 60 of the upper assembly 53 are clear of the previously aligned holes 16, fluid pressure is released in the motors 62 of the upper assembly, allowing the expansion springs 64 to urge the pins 60 of the upper pin assembly outwardly. Such pins 60 will then yieldably engage and slide on the inner wall of the outer caisson section until they register with the next lower openings or holes 16 therein. Each pin 60 then automatically engages such lower hole so as to lock the upper assembly 53 against movement relative to the outer caisson section. At the same time, the motors 68 are operated so as to stop the downward or retracting movement of their piston rods 70. Fluid pressure is then applied through the tubing 63 to the motors of the lower pin assembly 54 to retract its pins 60. The motors 68 are then operated to extend their piston rods 70 or permit such extension by the weight supported on the pins of the upper assembly 53, thus lowering the inner caisson section relative to the outer. As soon as each of the locking pins 60 in the lower pin assembly is clear of its previously aligned hole 16, fluid pressure is released from the motors 62 of the lower pin assembly so as to allow the expansion springs 64 associated therewith to urge the pins 60 against the inner wall of the outer section 13 of the caisson and into a hole 16, when moved into registration therewith, so as to again lock the sections together.

Extension of one or all of the inner sections is thus continued by the selective control of the fluid pressure means. To return the caisson sections to their nested is reversed.

fact that none of the various jacking mechanisms are mounted on the deck of the barge, provides the latter with deck working spacethat is unobstructed by either jacks or caissons. It also will be seen that when the sections of the caissons are in their stowed or nested position, they ofler very little or no resistance to the stability of the barge, yet are readily accessible and can easily be jacked down so as to be brought into firm bearing engagement with the marine ground at a minimum expenditure of time, labor, and cost. Conversely, the caisson sections are easily operable to assume their raised or nested position in the recess 27 of the barge.

The locking pins or bolts 36 and 66 releasably connect the caisson sections to the jacks so as selectively to control the vertical movement of the sections relative to the barge. When all the caissons are jacked down into firm engagement with the marine ground, the barge can be raised by the jack mechanism to the desired elevation and then is locked to the caissons, so as to be held firmly in a fixed position. The supply of fluid pressure to the upper andlower pin assemblies of each caisson section is preferably controlled from a master control panel on the deck of the barge through suitable valve means, so that the upper and lower locking pin assemblies of each caisson section cannot be disengaged at the same time. In the event the supply of fluid pressure to the jack should fail, for any reason, the springs associated with the reciprocating locking pins will automatically actuate these pins so that they engage in registered openings 16 in the caisson sections. Thus, means are provided for preventing the barge, when in its raised position, from accidentally being dropped either by failure of the jack mechanism or by human error. When the external and/or internal jacks have been actuated to lower the caisson in engagement with the ground, it will be seen that the external jack mechanisms 18 may then be operated, if necessary or in addition to the internal jacking mechanisms, to raise the barge above the level of the water to any desired height so as to convert the barge to a working platform. Manifestly, the external and internal pin jack assemblies and their associated telescopic cais'sons or columns may with equal efficiency be associated with land or other marine structures for various purposes and be installed at a minimum expenditure of time, labor, and cost.

It will be understood that the form of the invention shown is merely illustrative of preferred embodiments and that such changes may be made as come within the scope of the following claims.

I claim:

1. In combinations with a working platform having a vertical opening, a tubular telescopic column extending through said opening, said column including an outer section and at least one inner section, said outer section having vertically spaced holes, an external jack mechanism mounted on the platform adjacent saidopening, said jack mechanism having horizontally disposed locking pins arranged to engage said holes in said outer section when aligned therewith, an internal jack mechanism mounted on the upper end of said inner section and movable vertically in said outer section, said internal jack mechanism having horizontally disposed locking pins arranged to engage said holes in said outer section when.

aligned therewith, and fluid pressure operated means operatively connected to said locking pins for selectively moving the same.

'2. .In combination with a working platform having a vertical opening, a tubular telescopic column extending through said opening, said column including an outer section and an inner section, said outer section having vertically spaced pin holes, an external jack mechanism mounted on the platform adjacent said opening, said jack mechanism having an upper pin assembly and a lower pin assembly, each of said assemblies having-horizontally disposed pins movable inwardly through aligned holes in said outer section for connecting the same to the platform, power-operated means for moving the upper andlower pin assemblies vertically relative to each other, an internal jack mechanism mounted on the top of said inner section and movable vertically in said outer section, said internal jack mechanism including upper and lower pin assemblies having horizontally disposed locking pins movable outwardly through aligned holes in said outer section for locking the sections together, power-operated means for moving the upper and lower pin assemblies of the internal jack mechanism vertically relative to each other, and means including fluid pressure means operatively connected to said pins for moving said pins.

3. In combination with a working platform having a vertical opening, a tubular telescopic column extending through said opening, said column including an upper section, a lower section and at least one intermediate section, said upper and intermediate sections having vertically spaced holes, an external jack mechanism on the platform adjacent said opening, said jack mechanism having an upper pin assembly and a lower pin assembly, each of said assemblies having horizontally disposed pins movable inwardly through aligned holes in said upper section for connecting the same to the platform, fluid operating means between the upper and lower pin assemblies for moving the same vertically relative to each other, an in ternal jack mechanism on the intermediate section and on the lower end section, each internal jack mechanism including upper and lower pin assemblies having horizontally disposed locking pins movable outwardly through aligned holes in the section next above for locking the sections together, fluid pressure means between the upper and lower pin assemblies of the internal jack mechanisms for moving the same vertically relative to each other, means for controlling the flow of pressure fluid to the external and internal jack mechanisms, said means being operable to selectively control the relative vertical movement of the upper and lower pin assemblies of the external and internal jack mechanisms, fluid pressure means operatively connected to each pin assembly for moving the locking pins away from the section next above, and yieldable means connected to said locking pins for moving the same into locking'engagement with the section next above when the last mentioned fluid pressure means is released.

4. In combination with a floating barge having, a well opening, a tubular telescopic column extending through said opening, said column including an upper end section, at least one intermediate section and a lower end section, said upper end section and said intermediate section having vertical rows of pin holes, an external jack on the platform adjacent said vertical opening, said external jack including two vertical spaced sets of horizontally movable pins arranged to extend through'the holes in the upper section when in registration therewith, means for moving the pins into said holes, means for withdrawing the pins from the holes, the intermediate and the lower end sections of the caisson each having an internal jack mechanism movable in an adjacent upper section, each internal jack mechanism having two vertically spaced sets of horizontally disposed reciprocating locking pins arranged to extend into holes in the section next above when in registration therewith, means for actuating said last mentioned pins for moving them into looking, engagement 7 vertical opening, a tubular telescopic column extending through said opening, said column including an outer section having vertically spaced pin holes and an inner section, an external jack on the platform adjacent said opening, said jack having horizontally disposed locking pins movable inwardly through aligned holes in said outer section, an internal jack on the inner section and movable vertically in the adjacent outer section, said internal jack having upper and lower horizontally disposed locking pins movable outwardly through aligned holes in the outer section, fluid pressure means operatively connected to said locking pins for moving the same away from the outer section, yieldable means for urging each locking pin in engagement with the caisson when the fluid pressure means is released, and means for moving the upper and lower locking pins of the internal jack mechanism vertically relative to each other.

6. In combination with a floating barge having horizontally spaced vertical openings, a tubular telescopic caisson extending through each of said openings, each caisson including an outer section and at least one inner section, said outer section having vertical rows of pin holes, an external jack on the platform adjacent each opening, said jack having vertically spaced upper and lower locking assemblies provided with horizontally disposed reciprocating locking pins, means for moving said pins inwardly through aligned holes in the outer section, means for withdrawing the pins from said holes, an internal jack mechanism on the inner section and movable vertically in the adjacent outer section, said internal jack mechanism having a pair of upper and lower vertically spaced locking assemblies, each assembly having horizontally disposed pins movable outwardly into aligned holes in the outer section, and means for moving said last-mentioned pins into and out of aligned holes.

7. A floating barge as called for in claim 6 in which fluid operating means are positioned between and are connected to the upper and lower assemblies of each jack for moving the assemblies vertically relative to each other.

8. A floating assembly including a combined barge and working platform having vertical well openings, caissons extending through said openings, each of said caissons having telescopic sections, including an upper end section, at least one intermediate section telescoped therewithin and a lower end section telescoped within said intermediate section, said upper and intermediate sections being provided with vertically spaced pin openings, an external jack mechanism mounted in each well opening, said external jack mechanism including vertically spaced assemblies having horizontal pins arranged to extend through openings in the upper section of the caisson when in registration therewith, means for moving the pin assemblies vertically relative to each other when one assembly is released from the caisson, each of said intermediate and end sections of the caisson having an internal jack mechanism therein, each internal jack mechanism including vertically-spaced assemblies having horizontally disposed reciprocating pins, means for actuating said pins for moving them into locking engagement with an adjacent section, and means for moving the assemblies vertically relative to each other when the pins of one assembly are released.

9. In combination with a working platform having a vertical opening, a tubular telescopic column extending through said opening, said column including an outer section, an intermediate section and an inner section, said outer and intermediate sections having vertically spaced holes, an external jack on said platform, means for releasably connecting the external jack to said caisson, the intermediate and inner sections of the caisson each having an internal jack mechanism, each internal jack mechanism including vertically spaced upper and lower pin assemblies having horizontally disposed locking pins for releasably engaging the holes therein, fluid pressure means for moving the locking pins out of engagement with the caisson, and spring means formovin'g the locking pins in engagement with aligned holes when the pressure means is released.

10. A working platform as called forin claim 9 in which fluid operating means are positioned between the upper and lower assemblies for moving the same vertically relative to each other.

11. A working platform as called for in claim 9 in which the well opening on the barge is arranged to receive the sections of the caisson when the latter are in their stowed position.

12. A forcefully extensible and contractible support comprising: inner and outer elongated telescoping members, said inner member having an outer end and an inner end; a jacking mechanism disposed within said outer member for selectively effecting or restraining relative longitudinal movement in either direction between said members, said mechanism comprising a pair of longitudinally-spaced, fluid-pressure-actuated holding means each independently releasably engageable with said outer member against relative movement longitudinally thereof, and fluid pressure operated means connected to both of said holding means for selectively effecting or restraining relative movement therebetween in either direction longitudinally of said members, each of said holding means including a pin disposed substantially normal to the longitudinal axis of said members and mounted for projection into and retraction out of an aligned one of a longitudinal series of apertures in said outer member, and a fluid motor connected to said pin for controlling said projection and retraction thereof; and means mounting said jacking mechanism on said inner end of said inner member.

13. The structure defined in claim 12 in which the fluid pressure operated means comprises a double-acting hydraulic motor.

14. The structure defined in claim 12 in which the fluid pressure operated means comprises a double-acting hydraulic motor, and the mounting means includes means securing that one of the holding means adjacent the inner end of the inner member to said end.

15. In apparatus of the type described, the combination comprising: a platform; a plurality of telescopic columns for stably supporting said platform, each having an outer member and at least one inner member; guide means comprising wells extending through said platform mounting each of said outer members for substantially vertical movement in either direction relative to said platform; an exterior jacking mechanism mounted within said platform for each of said columns and mechanically engageable with said outer member thereof for selectively effecting or restraining said vertical movement in either direction and for positioning said outer member with its upper end substantially flush with the upper surface of said platform; and an interior jacking mechanism disposed within each of said outer members and mechanically engageable therewith and with the corresponding inner member for selectively eflfecting or restraining relative longitudinal movement in either direction between each outer member and its corresponding inner member, each of said interior jacking mechanisms comprising a pair of fluid-pressure-actuated holding means spaced longitudinally of the corresponding column and each independently releasably engageable with the corresponding outer member against relative movement longitudinally thereof and fluid-pressure-operated means connected to both of said holding means for selectively effecting or restraining relative movement therebetween in either direction longitudinally of said corresponding column, and including means mounting said interior jacking mechanism on the inner end of said corresponding inner member.

16. In apparatus of the type described, the combination comprising: a platform; a telescopic leg for supporting said platform including an outer section and at least one inner section having an outer end and an inner end; guide means on said platform mounting said outer section for substantially vertical movement in either direction relative to said platform; fluid-pressure actuated holding means carried by said inner end of said inner section and releasably engageable with said outer section for restraining relative longitudinal movement between said sections in either direction at least in either fully retracted or fully extended positions with respect to each other; a pair of relatively vertically movable holding means carried by said platform and releasably engageable with said outer section for restraining relative vertical movement in either direction between said outer section and said platform; and power-actuated means selectively operable, upon release of one of said holding means of said pair, to eflect relative vertical movement in either direction between said platform and said outer section or, upon release of said first-mentioned holding means, to effect relative longitudinal movement of said sections, between said fully retracted and extended positions.

17. The combination as defined in claim 16 wherein each of the holding means comprises a horizontally disposed pin movable into and out of engagement with a section.

18. The combination as defined in claim 17 wherein each of the sections includes at least upper and lower apertures for receiving a pin.

19. The combination as defined in claim 16, wherein the power-actuated means includes ram means operatively connected between the pair of holding means.

20. The combination as defined in claim 19 wherein the power-actuated means further includes second ram means connected with the said first-mentioned holding means and having a second holding means connected therewith for releasably engaging the outer section.

21. The combination as defined in claim 16 wherein the power-operated means includes a piston and cylinder unit acting between the sections for effecting the relative longitudinal movement therebetween.

22. A forcefully extensible and contractible support comprising: inner and outer telescoping members; first power-actuated holding means carried by said inner member and releasably engageable with said outer member for restraining relative longitudinal movement therebetween in either direction; second power-actuated holding means releasably engageable with said outer member, each of said holding means including a pin disposed substantially normal to the longitudinal axis of said member and mounted for projection into and retraction out of an aligned one of a longitudinal series of apertures in said outer member, and a fluid motor connected to said pin for controlling said projection and retraction thereof; power-actuated means extensible and retractable longitudinally of said members and connected with said second holding means; and means for connecting said poweractuated extensible and retractible means with said inner member, said power-actuated extensible and retractible means being operable upon release of said first holding means and engagement of said second holding means to etfect relative longitudinal movement between said members in either direction.

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